1 How do smoke detectors work?
Alpha particles ionise air in detector creating a current
When smoke enters alpha particles are blocked
2Why is gamma suitable for sterilisation of medical equipment?
It is most penetrating type of radiation
So it can irradiate all sides of the object
Object can stay in packaging
3How does food sterilisation using radiation work?
A gamma source is used to irradiate the food
This kills microorganisms on the food
Makes the food last longer and kills pathogens
4How does measuring thickness in factories using radiation work?
Material moves between beta source and detector
If material gets thicker, more beta will be absorbed, so less detected
If material gets thinner, less beta will be absorbed, so more detected
Machine makes adjustments to keep thickness constant
5Advantages and risks of isotopes with short half-lives
High activity so decays quickly - emits a lot of radiation in short amount of time
Advantage - If small amount used, will quickly lose radioactivity
Risk - Large amounts could make it extremely dangerous to handle
6 Advantages and risks of isotopes with long half-lives
Low activity do decays slowly - emits less radiation over a longer amount of time
Advantage - Handling is less dangerous
Risk - Contamination of environment possible for a much longer time
7What is radiotherapy?
Treatment of cancer using radiation
Bacteria and cancer cells are damaged more easily by radiation than healthy cells
Can be internal or external
8 How does external radiotherapy work?
Gamma rays are directed at cancerous tumour
Surrounding healthy cells are shielded to avoid damage
9 How does internal radiotherapy work?
Small amounts of radioactive material are inserted into tumour
Tumour is directly exposed to radiation and cancerous cells are killed.
10How do medical tracers work?
A person is injected with radioactive material
Tumours can be detected by tracking flow of material
11What isotopes are most appropriate for medical tracers and how much should be used?
Minimal amounts of gamma emitting isotopes with a short half life
‘Minimal amounts’ to reduce people’s exposure to radiation
‘Gamma emitting’ as is safest (least ionising) and can be detected outside the body (most penetrating)
‘Short half-life’ (around a few hours) so long enough to carry out procedure but decays before causing long-term harm
12Explain how Positron Emission Tomography (PET) Scanning works?
Person is injected with tracer emitting positrons.
Positrons travel small distance and annihilate when they interact with electrons
This produces a pair of gamma rays which are detected outside the body.
13Why do isotopes used for tracers and PET scans have to be produced nearby?
They have short half-lives of around a few hours (long enough to carry out procedure, but not long enough to cause long-term harm when injected)
Produced nearby so they will not have decayed too much by the time they reach hospital.
14 Advantages of nuclear power stations
Do not produce polluting gases (like carbon dioxide)
More energy per kg of fuel (compared to fossil fuels)
Highly reliable (for production of electricity)
15Disadvantages of nuclear power stations
Radioactive waste is dangerous and expensive to deal with
Nuclear meltdowns can be catastrophic to surrounding environment and people
Expensive start up and shut down costs
16Three nuclear reactions which can be a source of energy
Nuclear fusion
Nuclear fission
Radioactive decay
17 What is nuclear fission?
When a large, unstable nucleus splits into two smaller, daughter nuclei
18Fission of Uranium-235 (5 marks)
A neutron is absorbed by uranium-235
This makes uranium-236 which is very unstable and splits into…
Two smaller daughter nuclei AND 2 or 3 neutrons AND Gamma rays
Energy released is transferred to kinetic store of products
19What is the energy transfer in nuclear fission?
Energy transferred from the nuclear store of the nucleus
To the kinetic store of the products
20Which elements can be used for fission?
Uranium and plutonium
21Explain how a chain reaction can occur in a reactor
A uranium nucleus absorbs a neutron
The nucleus splits and releases neutrons
The neutrons are absorbed by more uranium nuclei
22Diagram of chain reaction
23In fission, what happens if there are excess neutrons?
Excess neutrons can speed up rate of reaction
More fission reactions can release excess energy
24What is meant by controlled nuclear fission?
One neutron is required for a fission reaction but 2 or 3 are produced
These can cause more fission reactions and produce more excess neutrons
Excess neutrons can speed up overall reaction
Control rods can absorb neutrons and slow down reaction
25Two things that need to be controlled for a reactor to keep running safely
Number of free neutrons
Energy of free neutrons
26What is the purpose of control rods in a nuclear reactor
To absorb excess neutrons
Control the rate of fission
27What are control rods usually made from?
Boron steel - can absorb neutrons without becoming unstable
28How can you control the rate of fission using control rods?
Lower the rods to decrease rate of fission - more neutrons absorbed
Raise the rods to increase rate of fission - less neutrons absorbed
Lower control rods all the way down to shut down reactor - all neutrons absorbed
29Why do fast-moving neutrons need to be slowed down?
Neutrons muist be travelling slowly to cause fission
If neutrons are too fast, they will not continue the chain reaction
30What is the purpose of the moderator in a nuclear reactor?
Slows down fast-moving neutrons produced by fission
So they can be absorbed by uranium nuclei
31What is the moderator usually made from and where is it?
Graphite/heavy water, around the fuel rods
32What is the purpose of the coolant in a nuclear reactor?
Prevents overheating
33What is the purpose of fuel rods in a nuclear reactor?
Contain uranium for fission
34What is the purpose of the shielding in a nuclear reactor?
Absorbs radiation
35 Explain how electricity is generated by a nuclear power station
Nuclear fission produces large amount of heat
Coolant carries away heat and heats a separate water source
The water turns to steam which drives a turbine
The turbine turns generators which produce electricity
36 Why is a separate water source used to generate electricity in a nuclear power station?
It reduces the risk of contamination
37Purpose of the nuclear reactor in generating electricity in a nuclear power station?
Provides thermal energy from fission chain reactions
38Purpose of the boiler in generating electricity in a nuclear power station?
Uses thermal energy to boil water and create steam
39 Purpose of the turbine in generating electricity in a nuclear power station?
Uses steam to transfer thermal energy into kinetic energy
40 Purpose of the generator in generating electricity in a nuclear power station?
Transfers kinetic energy into electrical energy
41Purpose of the condenser in generating electricity in a nuclear power station?
Cools the steam back into water
42Why are the products/waste of nuclear fission dangerous?
They are radioactive
And will stay radioactive for thousands of years
43Waste products of nuclear fission
Plutonium
Americium
Neptumium
44Why do you need to be careful when handling used up fuel rods?
They are extremely hot
45What happens to radioactive waste?
It is stored underground until its no longer harmful
46 Pros and cons of fusion reactors (in relation to waste)
Pro - little waste produced compared to energy generated
Con - The waste is extremely dangerous and expensive to handle
47 Where does fusion happen naturally?
In stars, like the sun
48What is the energy source of stars (like the sun)?
Nuclear fusion
49 Define nuclear fusion
When two small nuclei join together to produce a larger nucleus
50Why is the mass of the nucleus produced by nuclear fusion less than the sum of the individual particles?
Some of the mass is converted to energy and released
Due to mass-energy equivalence (E = mc2)
51Describe the fusion of two helium isotopes (tritium and deuterium)
At extremely high temperature and pressure
Two helium isotopes can fuse to produce helium (and an extra neutron)
The mass of the products is less than mass of reactants
Because some of the mass is converted to energy and released
To calculate the energy released, E = mc2
52Albert Einstein’s mass-energy equivalence formula
E = mc2
Energy(J) = mass(kg) x [speed of light(m/s)]2
53Speed of light
c = 3.0x108 m/s
54What is the difference between nuclear fusion and fission?
Nuclear fusion:
Two small nuclei join together to produce a larger nucleus
Occurs in stars
More energy released than in fission
Produces larger, stable (not radioactive) nuclei
Very high temperatures required
Nuclear fission:
One large nucleus splits into two smaller (daughter) nuclei
Occurs in nuclear reactors
Less energy released than in fusion
Produces smaller, radioactive nuclei and 2 or 3 neutrons
High temperatures and neutron required
55 What conditions are required for nuclear fusion?
Very high temperature and pressure/density
56Why does fusion not happen at low temperatures?
Protons in nuclei have positive charges and repel
Protons will only fuse if they get close enough to fuse
Very high temperature means very high kinetic energy
Which is required to overcome repulsion
57Why does fusion require high pressure/density?
(Even at high temperatures)
Collisions which are suitable for fusion are rare
High pressure/density increases the chance of suitable collisions
58 Why is fusion not used a source of power on Earth?
Fusion requires very high temperatures and pressures
These are difficult to achieve and maintain
Less energy produced by fusion than is required to start it